Dynamic frequency selection with discrimination

ABSTRACT

Dynamic frequency selection (DFS) is often a requirement for a wireless local area network (WLAN) apparatus to prevent the apparatus from interfering with other systems that have a priority to a radio frequency (RF) channel. When DFS is executed, the WLAN apparatus ceases WLAN operations on the channel and searches for an open channel to resume WLAN operations. Often a WLAN apparatus misinterprets signals from another system as operating on the channel when actually the received signals are signals leaked into the channel from a system transmitting on a different channel. Presented herein are methods and apparatuses for preventing unnecessary DFS operations resulting from misinterpreted signals through the use of a signal to noise ratio determined from a pulse spectral density of the received signal.

CROSS-REFERENCE TO RELATED APPLICATION

The present application is a continuation of U.S. patent applicationSer. No. 15/333,786, filed on Oct. 25, 2016, which is herebyincorporated by reference in its entirety.

TECHNICAL FIELD

The present disclosure relates to dynamic frequency selection (DFS) thatprevents wireless network traffic from interfering with other wirelesstraffic on a shared radio-frequency (RF) band.

BACKGROUND

The radiofrequency (RF) spectrum is a finite resource. As the number ofoperators (i.e., users) and applications have grown, some RF bands, suchas the Unlicensed National Information Infrastructure band (i.e., UNITband) or the Industrial, Scientific, and Medical band (i.e., ISM band)have been co-allocated for a variety of applications and users. Toprevent interference among the different applications, certain devicesare required to monitor co-allocated band channels and to take actionwhen interference is detected. In the United States, for example,wireless local area network (i.e., WLAN) devices (e.g., 802.11 a/hdevices) may operate in a 5 GHz band, which was traditionally allocatedfor use by radar (e.g., weather radar), but must tune to a differentchannel when interference is detected. This interference avoidanceprocess is referred to a Dynamic Frequency Selection (DFS).

Conventional DFS operations cause a wireless access point deviceoperating in a given channel to switch to another channel when apotential for interference (e.g., the presence of a radar signal) isdetected. Typically, a wireless device (e.g., wireless access point)running DFS continuously monitors (i.e., both prior to and duringchannel use) the channel of use (i.e., the service channel) for thepresence of a radar signal. Once detected, the device vacates and/orflags the channel as unavailable. Vacating a channel and relocating to anew channel is disruptive to communication and can result in the devicehaving to broadcast a channel switch announcement, disassociate withexisting client devices, search for a new channel, switch to the newchannel, and accept to new client associations.

Because radars typically transmit at high powers (e.g., between 250kilowatts and 1 megawatt), a radar may leak signals (e.g.,intermodulation products) into the service channel even when the radaris operating on a different channel. This situation may cause a falseDFS detection. This false DFS detection may unnecessarily trigger thewireless device to tune to another operating frequency or channel. Inaddition, false DFS detection (i.e., DFS falsing) can limit the numberof available channels when a device is searching for open channels.

In certain circumstances, it is desired that signals resulting fromradars operating on-channel be distinguished from signals resulting fromradars operating off-channel to reduce or eliminate unnecessary DFSoperations.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram illustrating an example WLAN network and a radarthat must not be interfered with according to an embodiment of thepresent disclosure.

FIG. 2A graphically illustrates an RF band having channels according toan embodiment of the present disclosure.

FIG. 2B graphically illustrates DFS that results from an on-channelsource (e.g., radar) according to an embodiment of the presentdisclosure.

FIG. 2C graphically illustrates prevention of DFS falsing that resultsfrom an off-channel source (e.g., radar) leaking signals into theservice channel according to an embodiment of the present disclosure.

FIGS. 3A and 3B graphically depict exemplary on-channel (FIG. 3A) andoff-channel (FIG. 3B) frequency estimation results according to anembodiment of the present disclosure.

FIG. 4 is a flow diagram for a method for preventing a wireless accesspoint (WAP) from performing unnecessary dynamic frequency selection(DFS) according to an embodiment of the present invention.

FIGS. 5A and 5B graphically depict the calculated power spectrumdensities (PSDs) of measured pulses from on-channel and off-channelradars.

FIGS. 6A and 6B graphically illustrate power spectrum density plots of apulse from an on-channel source (FIG. 4A) and from an off-channel source(FIG. 4B) according to an embodiment of the present disclosure.

FIGS. 7A and 7B graphically illustrate signal regions and noise regionsin PSD plots for a pulse from an on-channel source (FIG. 5A) and from anoff-channel source (FIG. 5B) according to an embodiment of the presentdisclosure.

FIG. 8 graphically depicts a block diagram of a wireless local areanetwork (WLAN) apparatus according to an embodiment of the presentdisclosure.

DESCRIPTION OF EXAMPLE EMBODIMENTS

Overview

Presented herein is a wireless device (e.g., wireless local area network(WLAN) apparatus, wireless access point, etc.) that is configured todiscriminate between interfering sources that are operating on theservice channel (i.e., on-channel) and interfering sources that areoperating on a different channel (i.e., off-channel) but leaking energyinto the service channel.

Such discrimination facilitates the wireless device in reducing falsepositives from, for example, a radar operating in-band but off-channel,which otherwise causes dynamic frequency selection operations (DFS) tooccur, thereby preventing such unnecessary dynamic frequency selection(DFS) operations. Because DFS operations disrupts communication, thereduction of unnecessary DFS operations (i.e., due to false positivetriggers) can improve network traffic throughput and wireless deviceuptime.

In an aspect, a method is disclosed for preventing a wireless accesspoint (WAP) device from performing unnecessary dynamic frequencyselection (DFS). The method includes receiving (i.e., by a processor) aradio-frequency (RF) signal on a first channel of the WAP; determining,by the processor, a signal-to-noise ratio (SNR) of a frequency spectrumderived from a portion of the received RF signal; comparing, by theprocessor, the SNR to an on-channel threshold associated with the firstchannel, wherein the SNR does not exceed the expected on-channelthreshold for a received RF signal transmitted by an RF source operatingon a second channel different from the first channel; and in response tothe comparison, preventing the WAP, operating in the first channel, fromperforming a DFS operation that causes the wireless access point deviceto tune to another channel.

In some embodiments, the SNR is determined by identifying (i.e., by theprocessor) a pulse within the portion of the received RF signal;computing (i.e., by the processor) a power spectral density (PSD) of thepulse; and determining the SNR of the PSD, wherein the SNR is determinedby relating (i) a signal portion of the PSD and (ii) a noise portion ofthe PSD that does not overlap with the first signal portion.

In some embodiments, the signal portion of the PSD contains a centerfrequency (Fc), wherein Fc is determined by estimating the frequency ofthe pulse.

In some embodiments, the signal portion of the PSD corresponds to thesignal occupied bandwidth (BW) of the pulse, wherein the BW isdetermined by estimated the duration of the pulse.

In some embodiments, the operation of computing a PSD of the pulseincludes computing the Fast Fourier Transform (FFT) of the pulse,wherein the FFT is comprised of FFT-bins.

In some embodiments, the operation of determining the SNR comprisesdetermining (i) an FFT-bin corresponding to an estimated centerfrequency (Fc) of the pulse, and (ii) the number of FFT-bins within anestimated signal occupied bandwidth (BW) of the pulse. Then, using theFFT-bin corresponding to Fc and the number of FFT-bins within the BW,the FFT-bins corresponding to the signal portion of the PSD and theFFT-bins corresponding to the noise portion of the PSD are determined.Next, a signal power is determined using the FFT-bins in the signalportion and a noise power is determined using the FFT-bins in the noiseportion. Finally, the SNR is determined as the ratio of the signal powerto the noise power.

In some embodiments, the FFT-bin that corresponds to Fc is at the centerof the FFT-bins corresponding to the signal portion of the PSD.

In some embodiments, the signal portion of the PSD spans the number ofthe FFT-bins within the BW of the pulse.

In some embodiments, determining a signal power using the FFT-bins inthe signal portion comprises summing the FFT-bins in the signal portionof the PSD, while determining a noise power using the FFT-bins in thenoise portion comprises summing the FFT-bins in the noise portion of thePSD.

In some embodiments, the method further comprises the operation ofretrieving, the on-channel threshold from a look-up table, wherein thelook-up table comprises a plurality of on-channel thresholds eachindexed by a given center frequency and/or a given signal-occupiedbandwidth.

In some embodiments, the method further comprises the operations ofcomparing (i.e., by a processor) the SNR to an on-channel thresholdassociated with the first channel and if the SNR exceed the on-channelthreshold, then causing the WAP, operating on the first channel, toperform a DFS operation, which causes the WAP to tune to anotherchannel.

In another aspect, a wireless device (e.g., a local area network (WLAN)apparatus), is disclosed. The wireless device includes an antennasubsystem tuned to a radio-frequency (RF) band; a transceiver subsystemconnected to the antenna subsystem and configured to transmit andreceive on a first channel, wherein the first channel is one of aplurality of channels in the RF band; and a processor communicativelycoupled to the transceiver subsystem and configured by instructions(e.g., program code stored in memory of the wireless device) to receivea signal from the transceiver subsystem and analyze a portion of thesignal to determine whether the portion of the signal is a pulse from aradar transmitting on the first channel or is noise from a radartransmitting on a channel other than the first channel. The analysis ofthe portion of the signal includes estimating a center frequency (Fc) ofthe portion of the signal; determining a power spectral density (PSD) ofthe portion of the signal; calculating a signal-to-noise ratio (SNR) ofthe power spectral density; comparing the SNR of the power spectraldensity to an on-channel threshold; and performing or not performing adynamic frequency operation to tune the transceiver to a second channelin the RF band based on the comparison of the SNR to the on-channelthreshold.

In some embodiments, if the SNR of the PSD exceeds the on-channelthreshold, the method includes performing the DFS operation that tunesthe transceiver subsystem to another channel (i.e., a second channel) inthe RF band; otherwise, the method includes remaining on the firstchannel.

In some embodiments, the noise is a pulse with nonlinear distortion froma radar transmitting on a channel other than the first channel.

In some embodiments, the instructions to determine the PSD of theportion of the signal comprises instructions that cause the processor tocompute a Fast-Fourier transform (FFT) of the portion of the signal,wherein the Fast-Fourier transform is comprised of FFT-bins.

In some embodiments, the instructions to calculate the SNR of the PSD,comprises instructions to (i) determine a signal region of the PSD,wherein the signal region is centered at Fc and spans a signal-occupiedbandwidth (BW); (ii) determine one or more noise regions of the PSD,wherein the one or more noise regions are regions in of the PSD not inthe signal region; (iii) compute a signal power from the signal regionand a noise power form the one or more noise regions; and (iv) calculatethe SNR as the ration of the signal power to the noise power.

In another aspect, a wireless local-area network apparatus is disclosed.The apparatus comprising: a (tunable) transceiver subsystem that istuned to a channel selected from a plurality of channels (e.g., in aband); a processor operatively coupled to the transceiver subsystem; anda memory having instructions (e.g., software) stored thereon. Theinstructions, when executed by the processor, cause the processor todetermine if a signal received by the transceiver is (i) from a radartransmitting on the channel or (ii) from a radar transmitting on adifferent channel and based on the determining adjusting the operationof the WLAN's dynamic frequency selection (DFS).

In some embodiments, upon determining that the signal is received from aradar transmitting on the channel, the DFS operates by searching for anopen channel and tuning the transceiver to the open channel.

In some embodiments, upon determining that the signal is received from aradar transmitting on a different channel, the DFS operates by remainingon the channel.

It is understood that throughout this specification the identifiers“first”, “second”, “third”, “fourth”, “fifth”, “sixth”, and such, areused solely to aid in distinguishing the various components and steps ofthe disclosed subject matter. The identifiers “first”, “second”,“third”, “fourth”, “fifth”, “sixth”, and such, are not intended to implyany particular order, sequence, amount, preference, or importance to thecomponents or steps modified by these terms.

Example Embodiment

FIG. 1 graphically illustrates an example WLAN 101 that includes anetwork WLAN apparatus 104 (e.g., a wireless access point) that isconfigured with a discrimination operation as disclosed herein. Asshown, the WLAN 101 includes a plurality of client wireless devices 102(shown as mobile devices 102 a, tablets 102 b, laptops 102 c, desktopcomputers 102 d, etc., that form communication links 103 with thenetwork WLAN apparatus 104. During operation, while the network WAPdevice 104 transmits information to, and receives information from, theclient WLAN devices 101, the network WAP device 104 is configured tomonitor on-channel signals to detect presence of a radar signal (e.g.,pulse) from a radar 105. Examples of such monitoring operations aredescribed in wireless protocols, such as specified by IEEE 802.11a,802.11n, 802.11ac, etc.

According to the protocols, in the United States and certain countries,a WAP may operate (i.e., transmit/receive) in some bands (e.g., 5 GHz)provided that the WAP does not interfere with other users 105 (e.g.,users with band priority) that also operate in this band (shown as radar105). To avoid interference with users 105 (e.g., radar) operating onthe same channel, the WAP device 104 is configured for dynamic frequencyselection (DFS). DFS operation is illustrated in FIGS. 2A and 2B.

FIGS. 2A and 2B illustrate example operations of dynamic frequencyselection (DFS) at a WLAN device in a local area network. As shown inFIG. 2A, an exemplary band 202 of a WAP device 104 includes a pluralityof channels (shown as channel “CH1 204”, channel “CH2 206”, channel “CH3208”, channel “CH4 210”, and channel “CH5 212”, though any number ofchannels may be employed). During operation, the WAP device 104 mayoperate on (i.e., within) one of these channels. As shown in thisexample and in FIG. 2A, the WLAN device 104 is operating on channel CH1204 and monitoring for a radar signal therein.

As shown in FIG. 2A, a radar device 105 operating on channel CH5 212causes no DFS operation, because no radar signal is detected on channelCH1 201. As a result, the WLAN device 104 continues to operate on CH1201.

Upon detecting that a radar 105 is operating on CH1 201, as shown inFIG. 2B, the WLAN device 104 is configured, via DFS, to search for a newand open channel in the band 202 on which to operate. In someembodiments, the search may include monitoring (e.g., for a period) oneor more other channels in the band (e.g., CH2 204, CH3 206, CH4 208, andCH5 208) for signals from other devices. Once an open channel is foundwithin the band 202, the WLAN device 104, in some embodiments,broadcasts a move announcement to client devices 102 connected to theWLAN device 104. The move announcement triggers the client devices 102to move from the current channel (namely, CH1 204) to an open channelspecified in the move announcement (e.g., one of channels CH2 206 to CH5212 as shown in FIG. 2B). The WLAN device 104, in some embodiments, thendisconnects the wireless links 103 with the client devices 102 onchannel CH1 204 and reestablishes the wireless links 103 with the clientdevices 102 on the new channel.

In some circumstances, signals detected by the WLAN device 104 arefalsely interpreted as originating from a radar source operating on thesame channel (i.e., on-channel) and DFS operations are carried outunnecessarily (i.e., DFS falsing). Radars, for example, transmit at veryhigh powers (e.g., 250 KW-1 MW) and despite filtering, may “leak”spurious signals (e.g., intermodulation products) into other channels,as shown in FIG. 2C. Specifically, FIG. 2C graphically illustratesprevention of DFS falsing that results from an off-channel source (e.g.,radar) leaking signals into the service channel. The power of theseleakage signals may be significant, especially when a receiver isproximate to the radar. As shown in FIG. 2C, an alias (i.e., ghost,false, etc.) radar 214 appears to be operating on CH1 204 because thespurious signals resemble the signals from a radar operating on-channel.

As shown in FIG. 2C, a WLAN device 104 with DFS discrimination operatingon channel CH1 204 detects spurious signals (e.g., intermodulationproducts) from a radar operating on CH5 212 but continues to operate onchannel CH1 204 without executing a DFS operation to tune the WLANdevice to another channel due to its ability to determine that thesignal received is from an off-channel radar 105.

It should be appreciated by one skilled in the art that the preventionof unnecessary DFS operation due to DFS falsing improves the throughputof the communication link 103 by eliminating unnecessary communicationdisruptions as well as effectively increasing the number of availablechannels in the band 202 to the WLAN device that would have becomeunavailable due to the false (i.e., alias, ghost, etc.) radar 214 thatis presumed to be operating on CH1 204.

Determining DFS falsing is complex because spurious signals (e.g.,intermodulation products) associated with an off-channel radar mayappear very similar to corresponding on-channel signals. For example,spurious signals from an off-channel radar may have the same pulse widthand pulse repetition rate as corresponding on-channel signals. Inaddition, it is also observed that the strength of a received pulse mayvary due to the distance that the signal has propagated before beingreceived by the WLAN device. For example, the signal strength ofspurious (i.e., leakage) pulses from radar at a first range (e.g.,nearby) may be comparable to the signal strength of on-channel pulsesfrom a radar at a second range (e.g., distant). In addition, it isobserved that pulses that are intermodulation products of an off-channelradar may have estimated center frequencies that appear stable. Thisstability is shown in FIGS. 3A and 3B. Specifically, FIGS. 3A and 3Billustrate frequency estimates (i.e., relative to the center frequencyof the channel) of signals in a channel as shown over time (i.e., duringa pulse). FIG. 3A shows the estimated frequency of a signal from a radarsignal that is on-channel (i.e., one that should cause DFS to occur),and FIG. 3B shows the estimated frequency of a signal from a radarsignal that is off-channel (i.e., one that may cause DFS falsing andwhere DFS should not occur). As shown in each of FIGS. 3A and 3B, thevariation of the estimated frequency for on-channel and off-channelsignals (i.e., shown within circled regions 302 a and 302 b) aresimilar.

FIG. 4 is a flow diagram for an example method for preventing DFSfalsing by a wireless access point (WAP) thereby preventing the WAP fromperforming unnecessary dynamic frequency selection (DFS) according to anembodiment of the present invention.

As shown in FIG. 4, the method 400, in some embodiments, begins withidentifying a pulse in a signal received by a WAP that is tuned to agiven channel (step 402). The pulse, in some embodiments, is extractedfrom the signal (step 404) and processed (e.g., sampled) to compute thepulse's power spectral density (PSD) (step 406). The signal to noiseratio (SNR) of the PSD is then calculated (step 408), and compared to anon-channel threshold (shown as “T”) (step 410). If the SNR is below theon-channel threshold then the device, in some embodiments, concludesthat the pulse is likely from a source operating off-channel. As aresult, DFS is not performed 412. In some embodiments, if the SNR isabove the on-channel threshold, then it is concluded that the pulse islikely from a source operating on-channel 414 and as a result, DFS isperformed 414. DFS may include the operations of ceasing transmission ona channel (i.e., the interfering channel) 416, tuning to the WAP to anew channel 418, and resuming transmitting/receiving (i.e., WAPoperations) on the new channel 420.

The identification of the pulse may include differentiating the pulsefrom other received signals. For example, a pulse may have a uniquepower, pulse width, pulse repetition frequency (PRF) that sets it apartfrom other signals. A received signal may processed to detect theseunique features and a portion of the signal containing the uniquefeatures (i.e., the pulse) may extracted. The portion of the signal mayalso be analyzed to determine the pulse's duration (Td) and the pulse'scenter frequency (Fc), which may further aid in extraction and/orcharacterization, as will be described in more detail below.

The extracted pulse typically includes a sequence of samples. To computethe PSD, a mathematical transformation is performed on the sequence ofsamples. For example, a fast Fourier transform (FFT) may be used tocompute the discrete Fourier transform of the sequence (i.e., totransform the pulse). The PSD that results from FFT is a finite sequenceof equally-spaced FFT-bins that (i) are distributed over a frequencyrange corresponding the sampling frequency of the pulse and (ii)collectively describe the distribution of the pulse's power versusfrequency. The length of the FFT corresponds to the number of FFT-bins(i.e., PSD resolution). The FFT length may vary and is typically chosenof sufficient length (e.g., 128) to discern the features (e.g., peaks,nulls, etc.) of the pulse, but not so long as to be computationallyexpensive (i.e., uses computational resources without providing moreinformation).

FIGS. 5A and 5B illustrate the calculated PDS's of measured pulses fromon-channel and off-channel radars. As shown in FIGS. 5A and 5B the mainlobe power levels of the PSD from on-channel and off-channel sources canbe comparable because of automatic gain control (AGC), which is oftenpresent in receivers. As a result, discriminating between pulses fromon-channel and off-channel sources generally requires an analysis of thePSD's features.

FIG. 6A illustrates the features (e.g., peaks, nulls, bandwidth, overallshape, etc.) of a typical PSD (i.e., spectrum) for a pulse from anon-channel radar. The individual FFT-bins are not shown, but one havingskill in the art will recognize that the PSD shown is technicallycomprised of a sequence of FFT-bins, as described previously. As aresult, the PSD's vertical axis corresponds with the power (e.g.,squared amplitude) of each frequency component (i.e., each FFT-bin),while the PSD's horizontal axis corresponds to frequency. The PSD of anon-channel pulse typically has a peak 600 at the pulse's centerfrequency (Fc). As a reference, the operating channel 602 is shown inFIG. 6A (and FIG. 6B). It should be noted that in typical operation, thecenter frequency of the pulse may not be aligned with the centerfrequency of the channel and the signal occupied bandwidth (i.e.,bandwidth) of the pulse 604 may only comprise a portion of the totalchannel bandwidth. Further, the pulse's bandwidth 604 may be measured ina variety of ways (e.g., 3 dB bandwidth, null-to-null bandwidth etc.).In addition, the pulse's bandwidth (i.e., the signal occupied bandwidth)typically corresponds to the pulse's duration (i.e., pulse width).

FIG. 6B illustrates a PSD typical of an unintentional signal leaked intothe service channel 602 from a source operating off-channel. Thesesignals (i.e., noise from the WAP's perspective) may be harmonics,intermodulation products, or other unintentional signals.Intermodulation products (i.e., intermodulation, intermods), forexample, are nonlinear distortions of signals when the signals arepassed through a nonlinear system. The nonlinear system may be an activedevice driven into nonlinearity (e.g., amplifier) or a normallynonlinear device (e.g., a mixer). In addition, passive circuits (e.g.,loose and/or corroded connectors), may also operate as nonlinearradiators in certain circumstances. Radar systems are especially proneto nonlinearities resulting in intermodulation products due to the highpowers that they transmit.

In contrast to FIG. 6A, the PSD from an off-channel source, shown inFIG. 6B, has a different spectrum. The differences include (but are notlimited to) the number of peaks, the number of nulls, the peak spacing,the center frequency, the signal occupied bandwidth, the amplitudevariation of peaks, the noise floor, and the overall shape (e.g., theshape of an envelope drawn from peak to peak). For example, theestimated center frequency of the off-channel pulse may appear betweenpeaks in the PSD. These differences are due, for example, to thenonlinearities inherent with intermodulation. Detection of thesedifferences facilitates the classification of a received pulse as eitherfrom an on-channel source (i.e., on-channel pulse) or from anoff-channel source (i.e., off-channel pulse).

To discriminate between on-channel and off-channel pulses, the examplemethod described previously embraces calculating a signal-to-noise ratio(SNR) of the PSD. The SNR provides a measure of the pulse's nonlineardistortion. This measurement may then be compared to a threshold todetermine if the source of the pulse (i.e., the radar) is operatingon-channel or off-channel. If the radar is operating on-channel, thenthe WAP may perform operations to vacate the channel in order to complywith federal or local regulations regarding spectrum use.

Computation of the SNR may be accomplished using operations tomathematically process a PSD obtained from a FFT of an extracted pulse.To start, the FFT-bin that corresponds with Fc (found through frequencyestimation) may be determined. In addition, the number of FFT-binscorresponding to the signal occupied bandwidth (BW) may be determinedusing the FFT length and the estimated pulse duration (Td) (e.g., foundduring pulse extraction). With this information, the FFT-binscorresponding to a signal region may be obtained. For example, if Ns isthe number of bins corresponding to the BW, and N_Fc is the FFT bincorresponding to the estimated center frequency, then the signal regionmay include the FFT-bins in the range of N_Fc-Ns to N_Fc+Nc.

The FFT-bins corresponding to the BW comprise the signal region of theFFT, while the other FFT-bins comprise the noise region of the FFT. As aresult, the PSD may be divided into a signal region and one or morenoise regions based. The division described may include assigning eachFFT-bin (i.e., bin) in the BW as a signal bin and assigning each bin innot in the BW as a noise bin. Alternatively, the groups may be formedfrom bins (i.e., samples) in the signal regions and noise region(s)respectively. Next, a signal power is computed from the signal region(i.e., from the values of the FFT-bins in the signal region) and a noisepower is computed from the one or more noise regions (i.e., from thevalues of the FFT-bins in these one or more noise regions).

Computing a power (e.g., signal power, noise power) from a region maycomprise summing the values of the bins in the region. In other words,an integration of the spectral components over a frequency range yieldsthe total power in the frequency range. Variations in the computation ofpower exist. For example, the square of each FFT-bin value may becomputed prior to summation. In another example, the average power maybe computed for the frequency range (i.e., summation of FFT-bins dividedby number of FFT-bins). All variations of computing and representing thepower of a signal region and a noise region are embraced by the presentdisclosure. After the power of the signal region and the noise region(or regions) is computed, the SNR may be calculated as the ratio of thesignal power to the noise power.

FIGS. 7A and 7B visually illustrate the SNR calculation process for theon-channel and off-channel PSDs described previously (i.e., FIGS. 6A and6B). The PSD for an on-channel pulse is illustrated in FIG. 7A. Thesignal region 700, in FIG. 7A, is the region containing the primary peak(i.e., main lobe). For the exemplary PSD shown in FIG. 7A the signalregion extends to nulls on either side of the main peak. The noiseregions 701 contain noise and/or secondary peaks not contained in thesignal region. To illustrate the power in the signal region 700 comparedto the power in the noise regions 701, the amplitude of the boxeshighlighting the regions are drawn to contain the peaks in each region.This illustration is for discussion purposes; the actual power may varyfor each region in practical implementations. The difference 702 betweenthe signal region and the noise regions (i.e., shown in FIG. 7A) isillustrative of the SNR for the on-channel PSD. FIG. 7B illustratescorresponding signal regions 703 and noise regions 704 for anoff-channel PSD. As shown, the difference 705 between the signal region703 and the noise regions 704 is illustrative of the SNR for theoff-channel PSD. As illustrated by FIGS. 7A and 7B, the on-channel SNR702 is greater than the off-channel SNR 705.

An on-channel threshold may be created so that pulses having PSD SNRsthat exceed the on-channel threshold determined to be from a radartransmitting on the operating channel, while pulses having PSD SNRs thatfail to exceed the on-channel threshold are determined to be from aradar transmitting on a different channel (and are leaking signal intothe channel). This determination may, in turn, facilitate the WAP takingsteps adjust the DFS (i.e., to respond to the pulse by moving operationsto an open channel or to ignore the pulse and remain operating on thechannel).

The on-channel threshold may be created from test data for a particularradar. For example, a plurality of on-channel thresholds may bedetermined from a plurality of radars. These thresholds may be stored ina look-up table (LUT) and indexed by characteristics of the radar (e.g.,Fc, Td, PRF, etc.) so that the operation of obtaining an on-channelthreshold (e.g., from a stored look-up table) occurs before the on/offchannel determination. For example, a pulse may be received and thepulse frequency (Fc), pulse duration (Td), and bandwidth (BW) may beestimated. The LUT may be queried using Fc and Td to obtain anon-channel threshold corresponding to a radar operating with one or moreof these characteristics.

Example Device

In another aspect, the present disclosure embraces a wireless local areanetwork (WLAN) apparatus (e.g., gateway, router, repeater, switch, hub,etc.), as shown in FIG. 8. The apparatus includes an antenna subsystem801 tuned to a radio-frequency (RF) band. The antenna subsystem 801 mayinclude a receiving/radiating element or elements (e.g., elements forbeamforming, elements for MIMO, etc.) that may be integrated with theapparatus or attached remotely to the apparatus by a waveguide (e.g.,coaxial cable). The antenna subsystem 801 may also include amplification(e.g., cable loss compensation) and circuitry (e.g., impedance matchingcircuits, harmonic filters, couplers, baluns, power combiners dividers,etc.) to improve the antenna subsystems operation (e.g., efficiency,signal routing, electromagnetic interference, etc.) with othersubsystems. The apparatus also includes a transceiver subsystem 802connected to the antenna subsystem. The transceiver subsystem includesthe electronics (e.g., RF amplifier, local oscillator, mixer, IFamplifier, IF filter, demodulator, baseband amplifier, ADC, DAC, etc.)to configure the subsystem to transmit and receive on one (i.e., a firstchannel) of a plurality of channels in the band. The apparatus alsoincludes a processor (e.g., CPU, multi-core processor, ARM, ASIC, FPGA,etc.) 803 communicatively coupled (e.g., via traces, system on a chip,etc.) to the transceiver subsystem 802. As used herein, processor refersto a physical hardware device that executes encoded instructions forperforming functions on inputs and creating outputs. In someembodiments, the processor may include analog-to-digital (ADC)converters (and digital-to-analog (DAC) converters) to communicate inanalog with the transceiver. The processor is configured by instructions(e.g., software, firmware, etc.) to perform WLAN operations (i.e.,802.11 communication) and signal discrimination for DFS. Theinstructions may be stored in a memory 804 communicatively coupled tothe processor (e.g., recalled from a non-transitory computer readablestorage media).

In one possible embodiment the instructions configure the processor togenerate a digital signal by digitizing a signal from the transceiverand then analyze the digital signal to determine whether a portion ofthe digital signal contains a signal from a radar transmitting on thefirst channel or noise from a radar transmitting on a channel other thanthe first channel. Similar to the previous discussion, the analysis ofthe digital signal includes estimating a center frequency (Fc) of theportion of the digital signal, determining a pulse width, anddetermining a PSD of the portion of the digital signal. The analysisfurther includes calculating a SNR of the PSD. The calculation of theSNR may include computing an FFT, determining the power in a signalregion and the power in one or more noise regions, and computing theratio of the signal power to the noise power. The SNR is then comparedto an on-channel threshold and a DFS operation to change channels iseither performed or not performed based on the comparison.

The analysis of the signal to determine if a signal is from anon-channel source or from an off-channel source may be executedindependently or as part of DFS. In other words, the analysis (i.e.,discrimination) algorithm may operate independently to control a DFSalgorithm, a set of DFS algorithms, or particular operations within aDFS algorithm. In addition, the analysis algorithm may operate inconjunction with other analysis algorithms. For example, a pluralityanalysis algorithms may processes the received signal to contribute aportion of information used to determine if DFS is required. In thiscase, the method described herein could return an SNR that whenconsidered along with other metrics returned by other algorithms todetermine the probability that the signal is from an on-channel sourceor an off-channel source. In addition, the analysis of the signal may berepeated (e.g., for multiple pulses) until a statistical model of theSNR is obtained and this statistical model of SNR may be compared to thethreshold.

The invention claimed is:
 1. A method for discriminating signals fordynamic frequency selection (DFS), the method comprising: receiving,using a wireless access point (WAP), a radio-frequency (RF) signal on afirst channel; determining a signal-to-noise ratio (SNR) of a frequencyspectrum derived from a portion of the received RF signal; comparing theSNR to an on-channel threshold associated with the first channel,wherein the on-channel threshold facilitates discriminating signalstransmitted by RF sources operating on the first channel from signalstransmitted by RF sources operating off the first channel; and upondetermining that the SNR does not exceed the on-channel threshold,preventing the WAP, operating on the first channel, from performing DFS.2. The method of claim 1, wherein determining a signal-to-noise ratio(SNR) of a frequency spectrum derived from a portion of the received RFsignal comprises: identifying a pulse within the portion of the receivedRF signal; computing a power spectral density (PSD) of the pulse; anddetermining the SNR of the PSD by relating a signal portion of the PSDand a noise portion of the PSD, wherein the signal portion and the noiseportion do not overlap.
 3. The method according to claim 2, wherein thesignal portion of the PSD contains a center frequency (Fc), wherein Fcis determined by estimating the frequency of the pulse.
 4. The methodaccording to claim 2, wherein the signal portion of the PSD correspondsto the signal occupied bandwidth (BW) of the pulse, wherein the BW isdetermined by estimating the duration of the pulse.
 5. The methodaccording to claim 2, wherein the computing a power spectral density(PSD) of the pulse, comprises: computing a fast Fourier Transform (FFT)of the pulse, wherein the FFT is comprised of FFT-bins.
 6. The methodaccording to claim 5, wherein determining the SNR of the PSD by relatinga signal portion of the PSD and a noise portion of the PSD comprises:determining an FFT-bin corresponding to an estimated center frequency(Fc) of the pulse and a number of FFT-bins within an estimated signaloccupied bandwidth (BW) of the pulse; determining, using the FFT-bincorresponding to Fc and the number of FFT-bins within the BW, FFT-binscorresponding to the signal portion and FFT-bins corresponding to thenoise portion; determining a signal power from the FFT-binscorresponding to the signal portion and a noise power from the FFT-binscorresponding to the noise portion; and determining the SNR as the ratioof the signal power to the noise power.
 7. The method according to claim6, wherein the FFT-bin corresponding to the Fc of the pulse is thecenter FFT-bin in the FFT-bins corresponding to the signal portion. 8.The method according to claim 6, the signal portion spans the number ofFFT-bins within the BW of the pulse.
 9. The method according to claim 6,wherein determining a signal power using the FFT-bins in the signalportion and a noise power using the FFT-bins in the noise portioncomprises: summing the FFT-bins in the signal portion of the PSD todetermine the signal power, and summing the FFT-bins in the noiseportion of the PSD to determine the noise power.
 10. The methodaccording to claim 1, further comprising: retrieving the on-channelthreshold from a look-up table, wherein the look-up table comprises aplurality of on-channel thresholds, each indexed by a given centerfrequency and/or a given signal-occupied bandwidth.
 11. The methodaccording to claim 1, further comprising: upon determining that the SNRexceeds the on-channel threshold, causing the WAP, operating on thefirst channel, to perform DFS.
 12. The method according to claim 1,wherein performing DFS comprises: ceasing the WAP'stransmitting/receiving on the channel; tuning the WAP to a new channel;and resuming the WAP's transmitting/receiving on the new channel.
 13. Awireless access point (WAP) with signal discrimination for dynamicfrequency selection (DFS), the WAP comprising: an antenna subsystemtuned to a radio-frequency (RF) band; a transceiver subsystem connectedto the antenna subsystem and configured to transmit and receive on afirst channel, wherein the first channel is one of a plurality ofchannels in the RF band; and a processor communicatively coupled to thetransceiver subsystem and configured by instructions to: receive an RFsignal on the first channel of the WAP, determine a signal-to-noiseratio (SNR) of a frequency spectrum derived from a portion of thereceived RF signal, comparing the SNR to an on-channel thresholdassociated with the first channel, wherein the on-channel thresholdfacilitates discriminating signals transmitted by RF sources operatingon the first channel from signals transmitted by RF sources operatingoff the first channel, and upon determining that the SNR does not exceedthe on-channel threshold, preventing the WAP, operating on the firstchannel, from performing DFS.
 14. The WAP according to claim 13, whereinto determine a signal-to-noise ratio (SNR) of a frequency spectrumderived from a portion of the received RF signal, the processor isconfigured by instructions to: identify a pulse within the portion ofthe received RF signal; compute a power spectral density (PSD) of thepulse; and determine the SNR of the PSD by relating a signal portion ofthe PSD and a noise portion of the PSD, wherein the signal portion andthe noise portion do not overlap.
 15. The WAP according to claim 14,wherein the signal portion of the PSD contains a center frequency (Fc),wherein Fc is determined by estimating the frequency of the pulse. 16.The WAP according to claim 14, wherein the signal portion of the PSDcorresponds to the signal occupied bandwidth (BW) of the pulse, whereinthe BW is determined by estimating the duration of the pulse.
 17. TheWAP according to claim 14, wherein to compute a power spectral density(PSD) of the pulse, the processor is configured by instructions to:compute a fast Fourier Transform (FFT) of the pulse, wherein the FFT iscomprised of FFT-bins.
 18. The WAP according to claim 17, wherein todetermine the SNR of the PSD by relating a signal portion of the PSD anda noise portion of the PSD that does not overlap with the signalportion, the processor is configured by instructions to: determine anFFT-bin corresponding to an estimated center frequency (Fc) of the pulseand a number of FFT-bins within an estimated signal occupied bandwidth(BW) of the pulse; determine, using the FFT-bin corresponding to Fc andthe number of FFT-bins within the BW, FFT-bins corresponding to thesignal portion of the PSD and FFT-bins corresponding to the noiseportion of the PSD; determine a signal power from the FFT-binscorresponding to the signal portion and a noise power from the FFT-binscorresponding to the noise portion; and determine the SNR as the ratioof the signal power to the noise power.
 19. The WAP according to claim13, wherein the processor is further configured by instructions to: upondetermining that the SNR exceeds the on-channel threshold, causing theWAP, operating on the first channel, to perform DFS.
 20. Anon-transitory computer readable storage medium containing computerreadable instructions that when executed by a processor of a wirelessaccess point (WAP) cause the processor to perform a method fordiscriminating signals for dynamic frequency selection (DFS), the methodcomprising: receiving a radio-frequency (RF) signal on a first channelof the WAP; determining a signal-to-noise ratio (SNR) of a frequencyspectrum derived from a portion of the received RF signal; comparing theSNR to an on-channel threshold associated with the first channel,wherein the on-channel threshold facilitates discriminating signalstransmitted by RF sources operating on the first channel from signalstransmitted by RF sources operating off the first channel; and upondetermining that the SNR does not exceed the on-channel threshold,preventing the WAP, operating on the first channel, from performing DFS.